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number theory intermediate

Problem

The positive integer divisors of 175, except 1, are arranged around a circle so that every pair of adjacent integers has a common factor greater than 1. What is the sum of the two integers adjacent to 7?
Solution
. To arrange the divisors of 175, we can (conveniently) start with the divisor 7. Since , the two divisors that are adjacent to 7 must be multiples of 7, which means they have to be and . Thus, the sum of the two integers adjacent to 7 is .
Final answer
210